This research project consists of clinical investigations of voice and speech in patients with Parkinson's disease before and after voice treatment. The long-range aims are to evaluate the efficacy of voice treatment for these patients and generate knowledge and hypotheses regarding the physiologic and neural mechanisms underlying voice and speech changes related to treatment as well as to progression of the disease. Specific aims are to (1) evaluate the interactive roles of the respiratory and laryngeal systems in treatment-related change; (2) document co-occurring changes in articulatory and velopharyngeal function within the context of an 'increased system effort' hypothesis; (3) evaluate the relationship between treatment-related changes and speech intelligibility; (4) evaluate the role of various patient factors in treatment effectiveness: (a) the short- and long-term effects of voice treatment for patients at various stages of Parkinson's disease, (b) the preventative role of early voice treatment for recently diagnosed patients, and (c) the role of patient suitability factors such as cognitive status and depression in treatment effectiveness; (5) evaluate the role of various treatment factors in treatment effectiveness: (a) the frequency and context of delivery, and (b) the comparative effectiveness of voice treatment and neuropharmacological treatment; and (6) develop a database on the voice and speech changes accompanying progression of Parkinson's disease. The following variables will be measured before and after therapy as well as longitudinally: respiratory (rib cage and abdominal) excursions, laryngeal resistance, subglottal pressure, vocal fold adduction, intensity, phonatory stability, articulatory gestures, velopharyngeal function, speech rate, intonation, speech intelligibility, and various perceptual features of voice. These investigations which address fundamental issues in voice treatment efficacy will have implications for the assessment and establishment of treatment models for patients with Parkinson's disease as well as for other neurological disorders.